sandbox: exynos: Move CONFIG_SOUND_MAX98095 to Kconfig

Move this over to Kconfig and tidy up.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/configs/snow_defconfig b/configs/snow_defconfig
index d8c01e6..0fd084b 100644
--- a/configs/snow_defconfig
+++ b/configs/snow_defconfig
@@ -11,3 +11,4 @@
 CONFIG_CMD_SOUND=y
 CONFIG_I2S=y
 CONFIG_I2S_SAMSUNG=y
+CONFIG_SOUND_MAX98095=y